The present invention relates to a device for injecting a cryogenic fluid into a chamber, under a pressure that is higher than the pressure in the chamber.
It is known to cool the content of a mixer or a kneader by introducing liquid CO2 or liquid nitrogen (LN2) at the base of the bowl of the mixer or kneader. The liquid CO2, introduced under pressure via an injection nozzle, is converted, upon its expansion, in the nozzle, to a solid (dry ice), and to a cold gas. The solid is mixed with the content of the mixer and cools it, but the cold gas also contributes to cooling by passing through the overall mass contained in the bowl.
A known device for implementing this method comprises a plurality of injection devices, disposed in the bottom of the bowl, and fed with liquid CO2 via a set of pipes, this set being provided with a single common control valve.
When the valve is closed, the liquid CO2 present in the pipes downstream of this valve cannot be removed very rapidly by the injection devices, and, when the pressure falls below about 5.18 bar in the pipes, it is converted to dry ice in these pipes, which are thereby clogged. It is therefore impossible to resume the injection as long as this dry ice has not disappeared by being converted to gas by heating.
It is possible to provide for the pipes connecting the valve to the injection devices to be flexible, thereby permitting dismantling, and in consequence, serving to accelerate the restart of the system. However, this dismantling is a relatively lengthy and arduous operation.
The same drawbacks subsist if, instead of a common valve for all the injection devices, a plurality of independent valves are provided, each connected to an injection device by a separate flexible pipe: in this case clogging occurs in the flexible pipe.
It has been found that the clogging occurs when the pressure of the liquid CO2 falls below 14 bar, which occurs fairly frequently when storage containers called “super-insulated” containers are used, such containers often being preferred in order to limit the heat losses.
A device for injecting into a chamber a liquid liable to solidify by expansion is known from document EP-A-376 823.
Patent EP-744 578 describes an injection device that overcomes the problems caused by clogging incidents in normal operating conditions. This device is such that the connection between the shutoff valve and the injection nozzle is calculated so that any slug formed in said connection and said nozzle following a closure of the injection valve can be expelled into the chamber by the pressurized liquid when the injection valve is reopened.
Thus the device does not comprise means for preventing the formation of the slug, but it is possible to expel this slug upon restart, so that a fresh injection can be carried out at any time after the end of a prior injection period. However, it proves that this device can be clogged by the entry of the material to be cooled in the injection device, so that the use of this device is limited to the cooling of a solid product.
A real need therefore exists for a device for injecting cryogenic fluid, a device that does not have the drawbacks encountered with the devices of the prior art and which is suitable for cooling any type of product, regardless of its physical state.